FOSSIL RECORD AND THE EVOLUTIONARY HISTORY OF INIODEA - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 204

more recently some authors consider the evidence supporting the assignment of Goniodelphis
to the Iniidae to be inconclusive. Muizon (1988c), in an exhaustive phylogenetic analysis of
both fossil and extant members of the infraorder Delphinida (defined as Lipotoidea + Iniodea
+ Delphinoidea; Muizon 1984), acknowledged the general similarity between Goniodelphis
and other iniids, but stated that the available material is too incomplete to confirm this
affiliation. Cozzuol (1996) followed Muizon's proposition, and considered the Iniidae as
strictly endemic from the South American fresh water systems.
Morgan (1994) reviewed the marine mammal fauna of the Bone Valley formation of
central Florida, from where the holotype and other specimens of Goniodelphis where found.
Despite the doubts expressed by other authors (Muizon, 1984; Cozzuol, 1996) he continued to
consider this species as an iniid. In the same paper, Morgan (1994: Figure 6A, B) described a
periotic (UF 135935) he referred to as an undetermined pontoporiid. Periotics of Pontoporia -
like species are actually present in the collection from the late Tertiary marine outcrops of the
East coast of North America deposited in the National Museum of Natural History,
Washington, DC (personal observation) and may well belong to S . russellae (see above).
However, in this particular specimen, the very small posterior process, lacking the laminated
posterior projection typical of Pontoporiidae and the more prominent and rounded superior
process, makes this specimen very close to the periotics of other iniids. It is quite similar to
one specimen from the ―Mesopotamiense‖ of Argentina, originally considered as
Pontoporiidae (Cozzuol, 1985) but lately correctly identified as Iniidae (Muizon, 1988a).
Two cranial traits can be used to identify an Iniidae. The knob-like elevated vertex and
the vomer separating the palatines and proximal part of the maxillaries, being continuously
exposed ventrally. Unfortunately, the vertex is not preserved in the holotype and this
character as not checked in the only known skull of G. hudsoni (Fig. 2). In the palate region,
despite the palatine bones being damaged, it is possible that the vomer is not continuously
exposed ventrally, so this trait is not present. The prenarial region of Goniodelphis is indeed
remarkably similar to other Iniidae.
The most convincing evidence of the presence of an iniid in a marine environment is
based on the periotic mentioned above. If this periotic really belongs to Goniodelphis, then
this genus may be included in the family, but the absence of some of the sinapomorphies
shared by the other known iniids suggest it may have a basal position in the clade.
Subfamily ISCHYRORHYNCHINAE Cozzuol, 1996
Genus Ischyrhorhynchus
I. vanbenedeni Ameghino, 1891
The taxonomic history of the genus Ischyrhorhynchus and its synonyms, Anisodelphis
and, in part, Saurodelphis, is quite confusing. The history is detailed by Pilleri & Gihr (1979)
and further clarified by Cozzuol (1985).